Electronic devices such as smartphones, tablets, and wearable computers are being miniaturized for the user's convenience, which in turn involves the miniaturization of electronic components in such devices. This includes digital cameras capable of producing digital images. While reducing form factors may increase user convenience, it often does so by sacrificing performance or quality.
With respect to digital cameras, slimmer form factors place lenses and filters so close to the camera's sensors that resulting digital images often have color artefacts and discolorations. Primary color restoration techniques to mitigate such effects and restore original colors are the lens shading correction (LSC), automatic white balancing (AWB), and sensor-to-standard color space conversion. Lens shading refers to attenuation of the image where the image is brighter near the center of the image and the edges of the image are darker. This attenuation varies among imaging sensor color channels and is mainly caused by optical system components when the light hits a camera sensor at steep (large) angles due to the short distance between the optics and the sensor. LSC is a technique used to compensate for such signal degradation. Since the amount of attenuation as well as a white point and a color space conversion matrix (CCM) are a function of the incoming light spectrum, the color restoration benefits from knowledge about the true illuminant to sufficiently eliminate the attenuation, calculate white point and color conversion, and in turn provide a good quality image. When the light source is unknown, or misestimated (i.e., the wrong light source is selected), the attenuation may not be adequately removed, and other noticeable severe discolorations may be visible on the image.